According to the current 3GPP specifications, in a location update procedure in inter-SGSNs in a case where a terminal is in idle mode, a processing in which the new SGSN gets bearers in a preservation state from the old SGSN is defined (non-patent literature 1). As for the types of bearers, there are PDP context for GPRS users and EPS context for EPS users, and the current 3GPP specifications describes getting these only by GTPv1 (GTP protocol, version 1) signals and GTPv2 (GTP protocol, version 2) signals (non-patent literatures 2 and 3) respectively.
FIGS. 8(A) and (B) illustrate the procedure of getting bearer information from an old SGSN to a new SGSN, where FIG. 8(A) illustrates a case of getting bearer information (PDP context) which is logical communication path information, using a GTPv1 signal to serve as a second protocol signal, and FIG. 8(B) illustrates a case of getting bearer information (EPS context), using a GTPv2 signal to serve as the first protocol signal.
As illustrated in FIG. 8(A), when a terminal UE in idle mode moves between SGSNs and sends a location update message to the new SGSN, the new SGSN gets the GPRS bearer information having been established on the old side, from the old SGSN. For this, the new SGSN requests bearer information to the old SGSN using a GTPv1 signal. Upon receiving the GTPv1 signal from the new SGSN, the old SGSN sets bearer information of the GPRS bearer that is currently established, in a response signal, and returns this response signal. The new SGSN gets the bearer information based on the bearer information set in the response signal from the old SGSN, and, based on the bearer information (PDP context), establishes a GPRS bearer between the new SGSN and the GGSN.
Also, as illustrated in FIG. 8(B), when the new SGSN gets EPS bearer information that is established between the old SGSN and the S-GW, the new SGSN requests bearer information to the old SGSN using a GTPv2 signal. Upon receiving the GTPv2 signal from the new SGSN, the old SGSN sets bearer information (EPS context) of the EPS bearer that is currently established, in a response signal, and returns this response signal. Based on the bearer information set in the response signal, the new SGSN establishes a new EPS bearer between the new SGSN and the S-GW.
By the way, to achieve interoperability between UMTS and EPS, an SGSN, which connects a terminal supporting UTRAN (W-CDMA/HSPA) to an EPC network, supports both a GTPv1 signal and a GTPv2 signal. Consequently, upon getting bearer information from the old SGSN, the bearer information is requested using either the GTPv1 signal or the GTPv2 signal.